You've made some excellent points like:
Truth will always stand up to scrutiny if it indeed is truth. Lies can only stand if the truth isn't allowed to be revealed.
Which are quite true and should hit hard if she thinks about it.
Towards the end of your note the quip jabbing her about God's name not being Jehovah is... uhhh... not entirely accurate.
Jehovah is as good as a name for God in English, as Jesus (DJEE-zuhz) is for Christ. Yahweh may be as good as Yeshua in pronouncing those names.
If you're going to say Yahweh, you might as well say Yeshua, or Yirmiyahu (for Jeremiah) or Yeshayahu (for Issaiah), and this would probably peg you as a Sacred Names Movement follower not a Jehovah's Witness.
If in Spanish you spell out Jesus like in English, but pronounce it "HEY-soos" it goes to show you how silly it sounds to insist on DJEE-zuhz but then say Yahweh. They are merely two different traditions, the one is an English names' tradition, the other is a modern scholarly tradition.
This may be news to all who disagree with this and insist on Yahweh. But...
In Hebrew it would never be pronounced like YA (as in yacht) with the second syllable WAY. In Biblical Hebrew the H was always pronounced, and that's why it was written. So if you don't aspirate the H's then you're not even close to how it may have been pronounced back then.
Josephus makes the point that it is pronounced as it is written. So look at how Judah (with Hebrew letters corresponding to YHWDH) and pronounced YEH-HOO-DAH, compares to Jehovah (YHWH) the D is the only difference. So if it was read as written just take out the D in YEH-HOO-DAH and you're left with YEH-HOO-AH.
Since Jehovah comes from Latin IEHOVAH, and IEHOVAH is a translitteration (alphabetic substitution) for YEH-HOO-AH then there's nothing wrong with using Jehovah and anyone who tells you different is just not well informed about the entire history and pronunciation of the Divine Name.
All right, now that I got that out of the way, I'd say redact the last paragraph and hit send if you want to hit hard, and probably distance her from you. But if not, then release a big sigh and hit delete instead.